Jockeys Hollie Doyle, Tom Marquand and Oisin Murphy took part in a protest by the British horse racing industry against the government's proposed tax rise on betting on the sport.
Leading jockeys, trainers and owners descended on Westminster to lobby MPs and show their opposition to possible changes, which the British Horseracing Authority (BHA) says would cost millions in revenue and lead to thousands of job losses.
The protest took place amid a one-day strike across British horse racing, with four meetings at Lingfield Park, Carlisle, Uttoxeter and Kempton Park being rescheduled by the BHA.
It is the first time the sport has voluntarily refused to race in its modern history.
Jockeys Paul O'Brien, Saffie Osborne, Kieran Shoemark, Lilly Pinchin and former rider Richard Johnson were also at Westminster.
They were all wearing 'Axe The Racing Tax' silks provided by the BHA, while there was also a statue of a horse with the same slogan.
The Treasury is proposing to introduce a single remote gambling tax, which would increase the 15% tax rate paid by bookmakers on racing and align it with online gambling, which is currently taxed at 21%.
The BHA says this would have a "destructive impact" on the industry, with its economic analysis predicting an estimated £330m loss in revenue and putting 2,752 jobs at risk in the first year alone.
"Racing has always been treated differently and, therefore, should continue to be treated differently because of the wider economic impact that British racing has," Louise Norman, chief executive of the Racehorse Owners Association (ROA) told BBC Radio 5 Live.
"This isn't about a game of chance - it is skillful. There is time, effort and contribution emotionally, financially across the sport, whether that's through the trainers, owners, jockeys, staff [and] the wider impacting relationships that racecourses have with communities.
"By unifying that approach, racing will be negatively and unfairly impacted."
The strike is taking place a day before the start of the four-day St Leger festival at Doncaster Racecourse.